Tubing made from strip metal stock



1958 A. J. SNlVELY v TUBING MADE FROM STRIP METAL STOCK Original Filed July 12, 1950 m Andrew J. 3

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2,866,480 TUBING MADE FROM STRIP METAL STOCK Andrew J. Suively, Bloomfield Township, Oakland County, Micln, assignor to Bundy Tubing Company, Detroit, Mich, a corporation of Michigan Original application July 12, 1950, Serial No. 173,205, now Patent No. 2,620,022, dated October 11, 1955. Divided and this application August 16, 1955, Serial No. 528,626

5 Claims. (Cl. 138- -74) This invention relates to tubing made from strip metal stock which is fashioned into tubular form with overlapping portions, the interfaces of which are bonded to gether to provide a fluid tight tubing. Thisapplication is a division of application Serial No. 173,295 filed July 12, 1950, now Patent Number 2,720,022 dated October 11, 1955.

The invention is concerned more particularly with tubing made from a single strip of bare metal stock wherein the bonding metal, in the form of a ribbon, is incorporated within the wall of the tubing as the strip is fashioned into tubing with continuous longitudinal movement. Subsequently, the tubing thus formed, with the bonding metal incorporated therein, is subjected to a heat treatment for melting the bonding metal. The bonding metal thus constitutes a reservoir which, upon becoming molten, supplies all requirements for bond metal for uniting the plies and the seam. The bonding metal, when molten, flows from the reservoir and fills in between the interfaces of the plies and seam to unite the same.

Among the objects of the invention is the provision of good strong tubing which can be produced at lower manufacturing costs on a production basis day in and day out with an exceedingly high percentage of good quality tubing thus eliminating wastefulness due to rejected tubing because of imperfections.

A further object of the invention is to produce tubing wherein the inside and outside surfaces are constituted by clean exposed surfaces of the bare strip stock of which the tube is made.

Other objects and advantages of the invention will become apparent as the following detailed description is considered.

Fig. l is a diagrammatic view illustrating a tube mill by which the tubing can be made in accordance with the invention.

Fig. 2 is an enlarged cross sectional view of the tubing after it is initially formed and while still in the cold state.

Fig. 3 is a view illustrating a furnace for heat treating the tubing.

Fig. 4 is a cross sectional view similar to Fig. 2 illustrating the finished tube after the heat treatment.

Fig. 5 isan enlarged partial cross sectional view showing the seam of the completed tubing.

other than steel, as for example Monel, may be used as the tube forming material, in which event a suitable bonding metal may be selected for the best or desired performance with strip other than steel.

Also in considering the invention it is believed that reference to the method by which the tubing is produced will be helpful. As the tubing is being formed a ribbon of copper is placed between the steel plies of a double walled tubing. Thus, the copper is originally furnished in a solid form, continuous for the length of the tubing. The copper is located between the plies so that upon becoming molten it quickly flows between the interfaces of the steel. It is important that'the dimensions of the ribbon be properly selected with reference to the size of the tubing involved and the amount of copper required to completely unite all portions of the interfaces. This is because a void or cavity remains in the tube wall after the molten copper has flowed from the reservoir.

The copper'ribbon thus embodied between the inner and outer plies constitutes a reservoir which supplies molten copperto the interfaces of the plies and seams.

Fig. 6 is an enlarged sectional view of a tube illustrat- 1 Upon becoming'molten thecopper flows quickly from the reservoir-and completely fills in between the interfaces. This action occurs by capillarity. The spacing between the interfacesis less than the cross dimension of the reservoir and thus flow by capillarity is promoted. Regardless of how tightly the interfaces are seated against each other, there is some space therebetween, and the fighter the plies are wrapped together the better because the molten copper seeks to flow into small spaces. It has been found that the limit of the capillary action of molten copper isabout .004 of an inch. When the cop per flows from the reservoir and in between the interfaces, it will not flow out of the seam. The flow stops at the peripheral surface of the tubing, thus securely uniting the interfaces completely unto the interior and exterior surfaces of the tubing. This capillary action occurs even though the dimension across the reservoir may be near or partly within the capillary limit of .004" because, even in a poorly wrapped tubing, that is, a tubing where the plies are not tightly compacted to gether, the spacing between the interfaces of the plies andin the seam is less than the cross dimension of the reservoir cavity.

By reference to Fig. 1, it will be seen that the strip steel stock may be in the form of a coil lfrom which the strip 2 is drawn and passed through a tube mill which has a plurality of forming rollers. Such tube mills are well known to those versed in the art and sufiice it here to indicate the tube mill generally by reference character 3. A mandrel 4, held by a suitable support '5, is introduced into the tubing while the strip is still open and this mandrel has an end portion 6 positioned between a pair 7 of opposing rollers of the tube mill to tightly compress the tube wall.

The tubing of the present invention, insofar as its structure is concerned, is illustrated in Fig. 2. The strip is fashioned through substantially 720 to provide an inner ply l0, and an outer ply 11 with the interfaces of the plies in substantial contact, as shown at 12. An intermediate portion of the strip is offset, preferably inan angular manner, as shown at 13, and the edges of the stock abut the opposite faces of the offset as shown at 14 and 15. The edge portions are preferably of bevelled formation to nicely fit against the offset. For convenience, this portion of the tubing namely, that portion constituted by the offset and the oppositely disposed abutting edges of the strip may herein be termed the seam. Tubing of this general construction fashioned from copper coated strip steel with the copper coating appearing both inside and outside the tube and with the plies and seam bonded by the copper has been produced in great quanti- Patented Dec. so, 1958) of the tubing, are securely bonded together with no burr or protrusion and with no open or unsealed portions because the copper flows up to the surfaces of the tubing and stops flowing at that location.

Still further, a tubing may be provided'with clean exposed steel surfaces both inside and out. This is desirable for some uses where copper or other bonding metal must be eschewed. Of course, a thin line of copper is present at the seam both inside and outside the tubing, but, where this is subject to attack by the fluids with which the tubing may be used, the attack occurs only for a very limited distance within the seam and then ceases. Of course, the finished tube may be coated or plated with other metal, such as tin or tin and lead alloy if desired.

The invention is especially directed to, and is applicable to, tubing fashioned from a single strip of stock with a double thickness wall. A tube thus formed definitely has a double wall formation throughout its circumference and therefore the strength of the tube is determined by the double wall. This differentiates from tubing made from two strips wherein the plies may not be in tight engagement and which, at some locations, unavoidably has a gap between the edges of the inner ply or the outer ply and therefore only a Wall of single thickness at the gap.

Notwithstanding the presence of the reservoir void, the tubing of the present invention definitely has a double wall formation throughout its circumferential extent. In addition, there is assurance that the interfaces of the plies and seam are bonded together throughout, except at the location of the reservoir void. It might be said that a concession is made in the presence of the reservoir void in order to obtain an unfailing bond of the interfaces. But overall conditions are improved. Faults and defects in the bond of the interfaces are practically eliminated. This is highly desirable because otherwise such faults and defects have great non-uniformity and cannot be determined in advance. As against this, the characteristics caused by the presence of the reservoir void are very uniform and can be controlled and determined in advance. This is highly desirable, particularly when it is considered that the tubing is made on a production basis with assur ance of a good bond between all the interfaces.

While the invention has been disclosed with reference to using only one ribbon of bonding material, it is within the invention to use two or more ribbons, but the use of one ribbon is generally preferred. However, for example, where it is the desire to make tubing with working prop erties suitable for some severe working conditions, it may be desirable to reduce the circumferential extent of the void, particularly in a tubing of larger diameter. This may be done by using two ribbons spaced circumferentially of the tubing and each having a width about /2 of the width of a single ribbon for supplying the same amount of copper and assuming that the thickness remains un changed. Thus while there are two resultant voids, the circumferential extent of each is proportionately reduced.

In some cases where the tubing is drawn for reduction purposes, and particularly where it is drawn through a die and over' a mandrel, the void may be partially or substantially closed, but it is considered to still exist 6 insofar as the herein disclosure and claims are concerned sinceeven though it be substantially closed there is no bond. The ribbon of bonding metal is referred to throughout the specification and some of the claims as being of copper. When the term copperfis thus used in the claims, it is used in a broad sense and is intended to cover not only commercially pure copper but other metals and alloys containing copper.

I claim:

1. A tubing comprising, a single strip of metal stock fashioned through substantially 720 into hollow cross sectional form with inner and outer plies disposed in interfacial relationship, the strip having an offset in an intermediate portion, the opposite edges of the strip being disposed in interfacial relationship with opposite sides of the olfset thereby providing a scam, the interfaces of the plies and the interfaces of the offset and said edges being secured together by a bonding metal having a melting point lower than that of the metal of the strip and having capillary thickness, said tubing having between its plies at a location circumferentially removed from the seam a repository for excess bonding metal extending lengthwise throughout the length of the tubing, said repository having a radial dimension which is greater than said capillary thickness of said bonding metal, said repository having a circumferential dimension, said radial dimension of said repository being such a small portion of the thickness of the tubing wall thereat and said circumferential dimension being such a small portion of the tubing circumference that the tubing wall has substantially the critical strength and working properties of the double thickness wall. I

2. The tubing defined in claim 1 wherein said radial dimension of said repository does not exceed substantially Ms of the thickness of the tubing wall and said circumferential dimension does not exceed substantially A the diameter of the tubing.

3. The tubing defined in claim 1 wherein at least one of said plies has a section of relatively thin metal incident to a recess in its interface, which cooperates with the opposing surface of the other ply to define said repository, said repository intersecting the interfaces between the plies.

4. The tubing as recited in claim 1 characterized in that both plies have a section of relatively thin metal incident to recesses in their interfaces, said thin sections being opposite each other so that the respective recesses are in facing relationship and define the said repository, said repository intersecting the interfaces between the plies.

5. The tubing as recited in claim 1 characterized in that the single strip is ferrous metal and the bonding metal is copper.

References Cited in the file of this patent UNITED STATES PATENTS 

